Torsional vibration dampers are employed extensively in internal combustion engines to reduce torsional vibrations delivered to rotatable shafts. The torsional vibrations may have a considerable amplitude and, if not abated, can potentially damage gears or similar structures attached to the rotatable shaft and cause fatigue failure of the rotatable shaft. Torsional vibration dampers absorb vibration and, to a certain extent, reduce the amplitude of the vibrations by converting the vibrational energy to thermal energy as a result of the damping action. The absorption of the vibrational energy lowers the strength requirements of the rotatable shaft and, therefore, lowers the required weight of the shaft. The torsional vibration damper also has a direct effect on inhibiting vibration of nearby components of the internal combustion engine which would be affected by the vibration.
Virtually all motor vehicles with internal combustion engines incorporate a “serpentine” drive belt system consisting of a single endless drive belt and a series of pulleys. The pulleys derive power from the endless drive belt and operate to drive the various vehicle accessories such as the engine fan, power steering pump, air pumps, air conditioning unit, and the alternator. The endless drive belt that drives each of these pulleys is driven by a drive pulley connected to the crankshaft of the internal combustion engine. To reduce the transfer of vibrations between the crankshaft and the serpentine drive belt system, the drive pulley may comprise a torsional vibration damper that functions to reduce the amplitude or magnitude of the angular vibrations delivered by the crankshaft.
Torsional vibration dampers can also be fixed to a drive shaft. The vibration damper can be fixed either to the interior surface of a hollow drive shaft or the exterior surface of a drive shaft.
The torsional vibration dampers all include an inertia mass fixed to a rotating member with a vibration absorbing material between the inertia mass and the rotating member. This elastomeric member absorbs torsional vibration. Generally, the elastomeric member is in compression between the inertia mass and the rotating member. The compression provides the requisite slip torque. Unfortunately, the compression also creates significant strain on the elastomeric member.
Low strains on the elastomeric member lead to a better fatigue life, whereas high contact pressures lead to improve slip torque. Generally, dampers have been engineered to balance the strains and slip torque or contact pressure such that a relatively long fatigue life is achieved with a correspondingly acceptable slip torque.